From: Xavier Noria <fxn@...>
Date: 2012-03-22T04:48:15+09:00
Subject: Re: What’s the best way to check if a feature/class has been loaded?

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On Wed, Mar 21, 2012 at 8:17 PM, Nikolai Weibull <now@bitwi.se> wrote:

> On Wed, Mar 21, 2012 at 16:43, Xavier Noria <fxn@hashref.com> wrote:
> > Ah, that won't work in 1.8.
> >
> > In 1.8 you can rely on the fact that const_defined? does not look into
> the
> > ancestors. I guess a portable solution will need to have code that
> depends
> > on the Ruby version.
>
> Or simply use my #feature? implementation.  But again, I would like to
> use something that I don=E2=80=99t have to copy&paste or require into eve=
ry
> project where I need this function.  Relying on ActiveSupport is
> definitely not an option.


OK, the implicit answer is that there is no built-in way to do that. You
need to write a short method like the ones we are mentioning.

Take into account that #feature? assumes the argument matches the constant
name, which may not be the case. For example

    module A
      module B
      end
    end

    module C
      D =3D A::B
    end

In that code A::B and C::D are defined constants that store the same module
object, but #feature? returns false on C::D.

It would be more correct to rely on const_defined? like Active Support does=
.

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On Wed, Mar 21, 2012 at 8:17 PM, Nikolai Weibull <span dir=3D"ltr">&lt;<a h=
ref=3D"mailto:now@bitwi.se" target=3D"_blank">now@bitwi.se</a>&gt;</span> w=
rote:<br><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">


<div><div>On Wed, Mar 21, 2012 at 16:43, Xavier Noria &lt;<a href=3D"mailto=
:fxn@hashref.com" target=3D"_blank">fxn@hashref.com</a>&gt; wrote:<br>
&gt; Ah, that won&#39;t work in 1.8.<br>
&gt;<br>
&gt; In 1.8 you can rely on the fact that const_defined? does not look into=
 the<br>
&gt; ancestors. I guess a portable solution will need to have code that dep=
ends<br>
&gt; on the Ruby version.<br>
<br>
</div></div>Or simply use my #feature? implementation. =C2=A0But again, I w=
ould like to<br>
use something that I don=E2=80=99t have to copy&amp;paste or require into e=
very<br>
project where I need this function. =C2=A0Relying on ActiveSupport is<br>
definitely not an option.</blockquote><div><br></div><div>OK, the implicit =
answer is that there is no built-in way to do that. You need to write a sho=
rt method like the ones we are mentioning.</div><div><br></div><div>Take in=
to account that #feature? assumes the argument matches the constant name, w=
hich may not be the case. For example</div>


<div><br></div><div>=C2=A0 =C2=A0 module A</div><div>=C2=A0 =C2=A0 =C2=A0 m=
odule B</div><div>=C2=A0 =C2=A0 =C2=A0 end</div><div>=C2=A0 =C2=A0 end</div=
><div><br></div><div>=C2=A0 =C2=A0 module C</div><div>=C2=A0 =C2=A0 =C2=A0 =
D =3D A::B</div><div>=C2=A0 =C2=A0 end</div><div><br></div><div>In that cod=
e A::B and C::D are defined constants that store the same module object, bu=
t #feature? returns false on C::D.</div>

<div><br></div><div>It would be more correct to rely on const_defined? like=
 Active Support does.</div><div><br></div>
<div><br></div></div>

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